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-rw-r--r--kernel/kcsan/debugfs.c349
1 files changed, 349 insertions, 0 deletions
diff --git a/kernel/kcsan/debugfs.c b/kernel/kcsan/debugfs.c
new file mode 100644
index 000000000000..023e49c58d55
--- /dev/null
+++ b/kernel/kcsan/debugfs.c
@@ -0,0 +1,349 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/atomic.h>
+#include <linux/bsearch.h>
+#include <linux/bug.h>
+#include <linux/debugfs.h>
+#include <linux/init.h>
+#include <linux/kallsyms.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <linux/sort.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+
+#include "kcsan.h"
+
+/*
+ * Statistics counters.
+ */
+static atomic_long_t counters[KCSAN_COUNTER_COUNT];
+
+/*
+ * Addresses for filtering functions from reporting. This list can be used as a
+ * whitelist or blacklist.
+ */
+static struct {
+ unsigned long *addrs; /* array of addresses */
+ size_t size; /* current size */
+ int used; /* number of elements used */
+ bool sorted; /* if elements are sorted */
+ bool whitelist; /* if list is a blacklist or whitelist */
+} report_filterlist = {
+ .addrs = NULL,
+ .size = 8, /* small initial size */
+ .used = 0,
+ .sorted = false,
+ .whitelist = false, /* default is blacklist */
+};
+static DEFINE_SPINLOCK(report_filterlist_lock);
+
+static const char *counter_to_name(enum kcsan_counter_id id)
+{
+ switch (id) {
+ case KCSAN_COUNTER_USED_WATCHPOINTS: return "used_watchpoints";
+ case KCSAN_COUNTER_SETUP_WATCHPOINTS: return "setup_watchpoints";
+ case KCSAN_COUNTER_DATA_RACES: return "data_races";
+ case KCSAN_COUNTER_ASSERT_FAILURES: return "assert_failures";
+ case KCSAN_COUNTER_NO_CAPACITY: return "no_capacity";
+ case KCSAN_COUNTER_REPORT_RACES: return "report_races";
+ case KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN: return "races_unknown_origin";
+ case KCSAN_COUNTER_UNENCODABLE_ACCESSES: return "unencodable_accesses";
+ case KCSAN_COUNTER_ENCODING_FALSE_POSITIVES: return "encoding_false_positives";
+ case KCSAN_COUNTER_COUNT:
+ BUG();
+ }
+ return NULL;
+}
+
+void kcsan_counter_inc(enum kcsan_counter_id id)
+{
+ atomic_long_inc(&counters[id]);
+}
+
+void kcsan_counter_dec(enum kcsan_counter_id id)
+{
+ atomic_long_dec(&counters[id]);
+}
+
+/*
+ * The microbenchmark allows benchmarking KCSAN core runtime only. To run
+ * multiple threads, pipe 'microbench=<iters>' from multiple tasks into the
+ * debugfs file. This will not generate any conflicts, and tests fast-path only.
+ */
+static noinline void microbenchmark(unsigned long iters)
+{
+ const struct kcsan_ctx ctx_save = current->kcsan_ctx;
+ const bool was_enabled = READ_ONCE(kcsan_enabled);
+ cycles_t cycles;
+
+ /* We may have been called from an atomic region; reset context. */
+ memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));
+ /*
+ * Disable to benchmark fast-path for all accesses, and (expected
+ * negligible) call into slow-path, but never set up watchpoints.
+ */
+ WRITE_ONCE(kcsan_enabled, false);
+
+ pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters);
+
+ cycles = get_cycles();
+ while (iters--) {
+ unsigned long addr = iters & ((PAGE_SIZE << 8) - 1);
+ int type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC :
+ (!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0);
+ __kcsan_check_access((void *)addr, sizeof(long), type);
+ }
+ cycles = get_cycles() - cycles;
+
+ pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles);
+
+ WRITE_ONCE(kcsan_enabled, was_enabled);
+ /* restore context */
+ current->kcsan_ctx = ctx_save;
+}
+
+/*
+ * Simple test to create conflicting accesses. Write 'test=<iters>' to KCSAN's
+ * debugfs file from multiple tasks to generate real conflicts and show reports.
+ */
+static long test_dummy;
+static long test_flags;
+static long test_scoped;
+static noinline void test_thread(unsigned long iters)
+{
+ const long CHANGE_BITS = 0xff00ff00ff00ff00L;
+ const struct kcsan_ctx ctx_save = current->kcsan_ctx;
+ cycles_t cycles;
+
+ /* We may have been called from an atomic region; reset context. */
+ memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));
+
+ pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters);
+ pr_info("test_dummy@%px, test_flags@%px, test_scoped@%px,\n",
+ &test_dummy, &test_flags, &test_scoped);
+
+ cycles = get_cycles();
+ while (iters--) {
+ /* These all should generate reports. */
+ __kcsan_check_read(&test_dummy, sizeof(test_dummy));
+ ASSERT_EXCLUSIVE_WRITER(test_dummy);
+ ASSERT_EXCLUSIVE_ACCESS(test_dummy);
+
+ ASSERT_EXCLUSIVE_BITS(test_flags, ~CHANGE_BITS); /* no report */
+ __kcsan_check_read(&test_flags, sizeof(test_flags)); /* no report */
+
+ ASSERT_EXCLUSIVE_BITS(test_flags, CHANGE_BITS); /* report */
+ __kcsan_check_read(&test_flags, sizeof(test_flags)); /* no report */
+
+ /* not actually instrumented */
+ WRITE_ONCE(test_dummy, iters); /* to observe value-change */
+ __kcsan_check_write(&test_dummy, sizeof(test_dummy));
+
+ test_flags ^= CHANGE_BITS; /* generate value-change */
+ __kcsan_check_write(&test_flags, sizeof(test_flags));
+
+ BUG_ON(current->kcsan_ctx.scoped_accesses.prev);
+ {
+ /* Should generate reports anywhere in this block. */
+ ASSERT_EXCLUSIVE_WRITER_SCOPED(test_scoped);
+ ASSERT_EXCLUSIVE_ACCESS_SCOPED(test_scoped);
+ BUG_ON(!current->kcsan_ctx.scoped_accesses.prev);
+ /* Unrelated accesses. */
+ __kcsan_check_access(&cycles, sizeof(cycles), 0);
+ __kcsan_check_access(&cycles, sizeof(cycles), KCSAN_ACCESS_ATOMIC);
+ }
+ BUG_ON(current->kcsan_ctx.scoped_accesses.prev);
+ }
+ cycles = get_cycles() - cycles;
+
+ pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles);
+
+ /* restore context */
+ current->kcsan_ctx = ctx_save;
+}
+
+static int cmp_filterlist_addrs(const void *rhs, const void *lhs)
+{
+ const unsigned long a = *(const unsigned long *)rhs;
+ const unsigned long b = *(const unsigned long *)lhs;
+
+ return a < b ? -1 : a == b ? 0 : 1;
+}
+
+bool kcsan_skip_report_debugfs(unsigned long func_addr)
+{
+ unsigned long symbolsize, offset;
+ unsigned long flags;
+ bool ret = false;
+
+ if (!kallsyms_lookup_size_offset(func_addr, &symbolsize, &offset))
+ return false;
+ func_addr -= offset; /* Get function start */
+
+ spin_lock_irqsave(&report_filterlist_lock, flags);
+ if (report_filterlist.used == 0)
+ goto out;
+
+ /* Sort array if it is unsorted, and then do a binary search. */
+ if (!report_filterlist.sorted) {
+ sort(report_filterlist.addrs, report_filterlist.used,
+ sizeof(unsigned long), cmp_filterlist_addrs, NULL);
+ report_filterlist.sorted = true;
+ }
+ ret = !!bsearch(&func_addr, report_filterlist.addrs,
+ report_filterlist.used, sizeof(unsigned long),
+ cmp_filterlist_addrs);
+ if (report_filterlist.whitelist)
+ ret = !ret;
+
+out:
+ spin_unlock_irqrestore(&report_filterlist_lock, flags);
+ return ret;
+}
+
+static void set_report_filterlist_whitelist(bool whitelist)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&report_filterlist_lock, flags);
+ report_filterlist.whitelist = whitelist;
+ spin_unlock_irqrestore(&report_filterlist_lock, flags);
+}
+
+/* Returns 0 on success, error-code otherwise. */
+static ssize_t insert_report_filterlist(const char *func)
+{
+ unsigned long flags;
+ unsigned long addr = kallsyms_lookup_name(func);
+ ssize_t ret = 0;
+
+ if (!addr) {
+ pr_err("KCSAN: could not find function: '%s'\n", func);
+ return -ENOENT;
+ }
+
+ spin_lock_irqsave(&report_filterlist_lock, flags);
+
+ if (report_filterlist.addrs == NULL) {
+ /* initial allocation */
+ report_filterlist.addrs =
+ kmalloc_array(report_filterlist.size,
+ sizeof(unsigned long), GFP_ATOMIC);
+ if (report_filterlist.addrs == NULL) {
+ ret = -ENOMEM;
+ goto out;
+ }
+ } else if (report_filterlist.used == report_filterlist.size) {
+ /* resize filterlist */
+ size_t new_size = report_filterlist.size * 2;
+ unsigned long *new_addrs =
+ krealloc(report_filterlist.addrs,
+ new_size * sizeof(unsigned long), GFP_ATOMIC);
+
+ if (new_addrs == NULL) {
+ /* leave filterlist itself untouched */
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ report_filterlist.size = new_size;
+ report_filterlist.addrs = new_addrs;
+ }
+
+ /* Note: deduplicating should be done in userspace. */
+ report_filterlist.addrs[report_filterlist.used++] =
+ kallsyms_lookup_name(func);
+ report_filterlist.sorted = false;
+
+out:
+ spin_unlock_irqrestore(&report_filterlist_lock, flags);
+
+ return ret;
+}
+
+static int show_info(struct seq_file *file, void *v)
+{
+ int i;
+ unsigned long flags;
+
+ /* show stats */
+ seq_printf(file, "enabled: %i\n", READ_ONCE(kcsan_enabled));
+ for (i = 0; i < KCSAN_COUNTER_COUNT; ++i)
+ seq_printf(file, "%s: %ld\n", counter_to_name(i),
+ atomic_long_read(&counters[i]));
+
+ /* show filter functions, and filter type */
+ spin_lock_irqsave(&report_filterlist_lock, flags);
+ seq_printf(file, "\n%s functions: %s\n",
+ report_filterlist.whitelist ? "whitelisted" : "blacklisted",
+ report_filterlist.used == 0 ? "none" : "");
+ for (i = 0; i < report_filterlist.used; ++i)
+ seq_printf(file, " %ps\n", (void *)report_filterlist.addrs[i]);
+ spin_unlock_irqrestore(&report_filterlist_lock, flags);
+
+ return 0;
+}
+
+static int debugfs_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, show_info, NULL);
+}
+
+static ssize_t
+debugfs_write(struct file *file, const char __user *buf, size_t count, loff_t *off)
+{
+ char kbuf[KSYM_NAME_LEN];
+ char *arg;
+ int read_len = count < (sizeof(kbuf) - 1) ? count : (sizeof(kbuf) - 1);
+
+ if (copy_from_user(kbuf, buf, read_len))
+ return -EFAULT;
+ kbuf[read_len] = '\0';
+ arg = strstrip(kbuf);
+
+ if (!strcmp(arg, "on")) {
+ WRITE_ONCE(kcsan_enabled, true);
+ } else if (!strcmp(arg, "off")) {
+ WRITE_ONCE(kcsan_enabled, false);
+ } else if (!strncmp(arg, "microbench=", sizeof("microbench=") - 1)) {
+ unsigned long iters;
+
+ if (kstrtoul(&arg[sizeof("microbench=") - 1], 0, &iters))
+ return -EINVAL;
+ microbenchmark(iters);
+ } else if (!strncmp(arg, "test=", sizeof("test=") - 1)) {
+ unsigned long iters;
+
+ if (kstrtoul(&arg[sizeof("test=") - 1], 0, &iters))
+ return -EINVAL;
+ test_thread(iters);
+ } else if (!strcmp(arg, "whitelist")) {
+ set_report_filterlist_whitelist(true);
+ } else if (!strcmp(arg, "blacklist")) {
+ set_report_filterlist_whitelist(false);
+ } else if (arg[0] == '!') {
+ ssize_t ret = insert_report_filterlist(&arg[1]);
+
+ if (ret < 0)
+ return ret;
+ } else {
+ return -EINVAL;
+ }
+
+ return count;
+}
+
+static const struct file_operations debugfs_ops =
+{
+ .read = seq_read,
+ .open = debugfs_open,
+ .write = debugfs_write,
+ .release = single_release
+};
+
+void __init kcsan_debugfs_init(void)
+{
+ debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops);
+}

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